Clutch device

ABSTRACT

A clutch device includes a pressure plate movable toward or away from a clutch center and rotatable relative to the clutch center to press input-side rotating plates and output-side rotating plates. The clutch center includes center-side cam portions each including a center-side assist cam surface. At least one of the center-side cam portions includes at least one of a first center-side recess recessed in a first direction from a surface of center-side cam portion at a side of a second direction or a second center-side recess recessed in the second direction from a surface of the center-side cam portion at a side of the first direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent No.2022-116636 filed on Jul. 21, 2022 and Japanese Patent No. 2022-195700filed on Dec. 7, 2022. The entire contents of these applications arehereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a clutch device. More particularly,the present disclosure relates to a clutch device that arbitrarilyallows or interrupts transfer of a rotation driving force of an inputshaft, which is rotationally driven by a prime mover such as an engine,to an output shaft.

2. Description of the Related Art

Conventional vehicles such as motorcycles include clutch devices. Aclutch device is disposed between an engine and a drive wheel and allowsor interrupts transfer of a rotation driving force of the engine to thedrive wheel. The clutch device generally includes a plurality ofinput-side rotating plates that rotate by a rotation driving force of anengine and a plurality of output-side rotating plates connected to anoutput shaft that transfers the rotation driving force to a drive wheel.The input-side rotating plates and the output-side rotating plates arealternately arranged in a stacking direction, and the input-siderotating plates and the output-side rotating plates are brought intopressure contact with each other and are separated from each other sothat transfer of a rotation driving force is allowed or interrupted.

Japanese Patent No. 5847551 and International Patent Publication No.2018/172176, for example, disclose clutch devices each including aclutch center (clutch member) that holds output-side rotating plates(driven-side clutch plates), and a pressure plate (pressure member)movable toward or away from the clutch center. The pressure plate isconfigured to press the input-side rotating plates and the output-siderotating plates. In this manner, the clutch device includes an assemblyof the clutch center and the pressure plate.

A clutch center and a pressure plate of each of the clutch devicesdescribed in Japanese Patent No. 5847551 and International PatentPublication No. 2018/172176 include an assist cam surface that generatesa force in a direction of causing the pressure plate to approach theclutch center in a state where a rotation driving force of an engine canbe transferred to an output shaft, to increase a pressing force betweeninput-side rotating plates and output-side rotating plates, and aslipper cam surface that moves the pressure plate away from the clutchcenter to reduce a pressing force between the input-side rotating platesand the output-side rotating plates when the rotation speed of theclutch center exceeds the rotation speed of the pressure plate.

Cam portions of the clutch center and the pressure plate including theassist cam surface and the slipper cam surface are relatively thick.Thus, as the cam portions become large, the weight thereof increases,resulting in a problem of an increase in the weight of the entire clutchdevice. Since the clutch device is mounted on a vehicle such as amotorcycle, the clutch device is preferably relatively lightweight.

SUMMARY OF THE INVENTION

Preferred embodiments of the present disclosure provide clutch deviceseach capable of achieving weight reduction of cam portions including anassist cam surface and a slipper cam surface in at least one of a clutchcenter or a pressure plate.

A clutch device according to a preferred embodiment of the presentdisclosure is a clutch device to allow or interrupt transfer of arotation driving force of an input shaft, and includes a clutch centerhoused in a clutch housing holding a plurality of input-side rotatingplates, holding a plurality of output-side rotating plates alternatelyarranged with the input-side rotating plates, and operable to berotationally driven together with the output shaft, the input-siderotating plates being operable to be rotationally driven by rotationaldriving of the input shaft, and a pressure plate movable toward or awayfrom the clutch center and rotatable relative to the clutch center topress the input-side rotating plates and the output-side rotatingplates. The clutch center includes an output shaft holding portion towhich the output shaft is coupled, and a plurality of center-side camportions located radially outward of the output shaft holding portionand each including a center-side assist cam surface operable to generatea force in a direction of causing the pressure plate to approach theclutch center in order to increase a pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the pressure plate. Assuming a direction in whichthe pressure plate approaches the clutch center is a first direction,and a direction in which the pressure plate moves away from the clutchcenter is a second direction, at least one of the center-side camportions includes at least one of a first center-side recess or a secondcenter-side recess, the first center-side recess being recessed in thefirst direction from a surface of the center-side cam portion at a sideof the second direction, the second center-side recess being recessed inthe second direction from a surface of the center-side cam portion at aside of the first direction.

In a clutch device according to a preferred embodiment of the presentdisclosure, at least one of the center-side cam portions includes atleast one of the first center-side recess that is recessed in the firstdirection from the surface of the center-side cam portion at the side ofthe second direction or the second center-side recess that is recessedin the second direction from the surface of the center-side cam portionat the side of the first direction. In this manner, since at least oneof the center-side cam portions includes at least one of the firstcenter-side recess or the second center-side recess, the center-side camportions are more lightweight than those not including these recesses.Since the clutch device includes the more lightweight clutch center,weight reduction of the entire clutch device is achieved.

A clutch device according to another preferred embodiment of the presentdisclosure is a clutch device to allow or interrupt transfer of arotation driving force of an input shaft, and includes a clutch centerhoused in a clutch housing holding a plurality of input-side rotatingplates, holding a plurality of output-side rotating plates alternatelyarranged with the input-side rotating plates, and operable to berotationally driven together with the output shaft, the input-siderotating plates being operable to be rotationally driven by rotationaldriving of the input shaft, and a pressure plate movable toward or awayfrom the clutch center and rotatable relative to the clutch center topress the input-side rotating plates and the output-side rotatingplates. The pressure plate includes a plurality of pressure-side camportions located radially outward of the output shaft and each includinga pressure-side assist cam surface operable to generate a force in adirection of causing the pressure plate to approach the clutch center inorder to increase a pressing force between the input-side rotatingplates and the output-side rotating plates upon rotation relative to theclutch center. Assuming a direction in which the pressure plateapproaches the clutch center is a first direction, and a direction inwhich the pressure plate moves away from the clutch center is a seconddirection, at least one of the pressure-side cam portions includes atleast one of a first pressure-side recess or a second pressure-siderecess, the first pressure-side recess being recessed in the seconddirection from a surface of the pressure-side cam portion at a side ofthe first direction, the second pressure-side recess being recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction, and when seen in an axial direction of theoutput shaft, at least a portion of the first pressure-side recessoverlaps with the pressure-side assist cam surface.

In a clutch device according to a preferred embodiment of the presentdisclosure, at least one of the pressure-side cam portions includes thefirst pressure-side recess that is recessed in the second direction fromthe surface of the pressure-side cam portion at the side of the firstdirection or the second pressure-side recess that is recessed in thefirst direction from the surface of the pressure-side cam portion at theside of the second direction. In this manner, since at least one of thepressure-side cam portions includes at least one of the firstpressure-side recess or the second pressure-side recess, thepressure-side cam portions are more lightweight than those not includingthese recesses. Since the clutch device includes the more lightweightpressure plate, weight reduction of the entire clutch device isachieved.

Preferred embodiments of the present disclosure provide clutch deviceseach capable of achieving weight reduction of cam portions including anassist cam surface and a slipper cam surface in at least one of a clutchcenter or a pressure plate.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a clutch device according to onepreferred embodiment of the present invention.

FIG. 2 is a perspective view of a clutch center according to onepreferred embodiment of the present invention.

FIG. 3 is a plan view of a clutch center according to one preferredembodiment of the present invention.

FIG. 4 is a perspective view of a clutch center according to onepreferred embodiment of the present invention.

FIG. 5 is a plan view of a clutch center according to one preferredembodiment of the present invention.

FIG. 6 is a perspective view of a pressure plate according to onepreferred embodiment of the present invention.

FIG. 7 is a plan view of a pressure plate according to one preferredembodiment of the present invention.

FIG. 8 is a perspective view of a pressure plate according to onepreferred embodiment of the present invention.

FIG. 9 is a plan view of a pressure plate according to one preferredembodiment of the present invention.

FIG. 10 is a side view of a pressure plate according to one preferredembodiment of the present invention.

FIG. 11 is a plan view illustrating a state where a clutch center and apressure plate according to one preferred embodiment of the presentinvention are combined.

FIG. 12 is a plan view illustrating a state where a clutch center and apressure plate according to one preferred embodiment of the presentinvention are combined.

FIG. 13A is a schematic view for describing effects of a center-sideassist cam surface and a pressure-side assist cam surface.

FIG. 13B is a schematic view for describing effects of a center-sideslipper cam surface and a pressure-side slipper cam surface.

FIG. 14 is a cross-sectional view of a center-side cam portion accordingto one preferred embodiment of the present invention.

FIG. 15 is a cross-sectional view of a pressure-side cam portionaccording to one preferred embodiment of the present invention.

FIG. 16 is a disassembled perspective view of a clutch center and apressure plate according to another preferred embodiment of the presentinvention.

FIG. 17 is a plan view of a clutch center according to another preferredembodiment of the present invention.

FIG. 18 is a perspective view of a pressure plate according to anotherpreferred embodiment of the present invention.

FIG. 19 is a plan view of a pressure plate according to anotherpreferred embodiment of the present invention.

FIG. 20 is a plan view of a clutch center according to a variation of apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Clutch devices according to preferred embodiments of the presentdisclosure will be described hereinafter with reference to the drawings.The preferred embodiments described herein are, of course, not intendedto particularly limit the present disclosure. Elements and featureshaving the same functions are denoted by the same reference characters,and description for the same elements and features will not be repeatedor will be simplified as appropriate.

First Preferred Embodiment

FIG. 1 is a cross-sectional view of a clutch device 10 according to thispreferred embodiment. The clutch device 10 is provided in a vehicle suchas a motorcycle, for example. The clutch device 10 allows or interruptstransfer of a rotation driving force of an input shaft (crankshaft) ofan engine of the motorcycle to an output shaft 15, for example. Theclutch device 10 allows or interrupts transfer of a rotation drivingforce of the input shaft to a drive wheel (rear wheel) through theoutput shaft 15. The clutch device 10 is disposed between the engine anda transmission.

In the following description, directions in which a pressure plate 70 ofthe clutch device 10 moves toward and away from the clutch center 40will be referred to as directions D, a direction in which the pressureplate 70 moves toward the clutch center 40 will be referred to as afirst direction D1, and a direction in which the pressure plate 70 movesaway from the clutch center 40 will be referred to as a second directionD2. Circumferential directions of the clutch center 40 and the pressureplate 70 will be referred to as circumferential directions S, one of thecircumferential direction S from one pressure-side cam portion 90 toanother pressure-side cam portion 90 (direction from one center-side camportion 60 to another center-side cam portion 60) will be referred to asa first circumferential direction S1 (see FIG. 7 ), and one of thecircumferential direction S from the other pressure-side cam portion 90to the one pressure-side cam portion 90 (direction from the othercenter-side cam portions 60 to the one center-side cam portions 60) willbe referred to as a second circumferential direction S2 (see FIG. 7 ).In this preferred embodiment, axial directions of the output shaft 15,axial directions of a clutch housing 30, axial directions of the clutchcenter 40, and axial directions of the pressure plate 70 are the same asthe directions D. The pressure plate 70 and the clutch center 40 rotatein the first circumferential direction S1 (i.e., direction from acenter-side assist cam surface 60A to a center-side slipper cam surface60S in one center-side cam portion 60). It should be noted that thedirections described above are defined simply for convenience ofdescription, and are not intended to limit the state of installation ofthe clutch device 10 and do not limit the present disclosure.

As illustrated in FIG. 1 , the clutch device 10 includes the outputshaft 15, input-side rotating plates 20, output-side rotating plates 22,the clutch housing 30, the clutch center 40, the pressure plate 70, anda stopper plate 100.

As illustrated in FIG. 1 , the output shaft 15 is a hollow shaft. Oneend of the output shaft 15 rotatably supports an input gear 35 describedlater and the clutch housing 30 through a needle bearing 15A. The outputshaft 15 fixedly supports a clutch center 40 through a nut 15B. That is,the output shaft 15 rotates together with the clutch center 40. Theother end of the output shaft 15 is coupled to a transmission (notshown) of an automobile, for example.

As illustrated in FIG. 1 , the output shaft 15 includes, in a hollowportion 15H thereof, a push rod 16A and a push member 16B adjacent tothe push rod 16A. The hollow portion 15H serves as a channel of clutchoil. Clutch oil flows in the output shaft 15, that is, in the hollowportion 15H. The push rod 16A and the push member 16B are slidable inthe hollow portion 15H of the output shaft 15. The push rod 16A has oneend (left end in the drawing) coupled to a clutch operation lever (notshown) of the motorcycle, and slides in the hollow portion 15H byoperation of the clutch operation lever and presses the clutch pushmember 16B in the second direction D2. A portion of the push member 16Bprojects outward of the output shaft 15 (in the second direction D2 inthis preferred embodiment) and is coupled to a release bearing 18provided on the pressure plate 70. The push rod 16A and the push member16B are thinner than the inner diameter of the hollow portion 15H sothat flowability of clutch oil is obtained in the hollow portion 15H.

The clutch housing 30 is made of an aluminum alloy. The clutch housing30 has a bottomed cylindrical shape. As illustrated in FIG. 1 , theclutch housing 30 includes a bottom wall 31 having a substantiallycircular shape, and a side wall 33 extending from an edge of the bottomwall 31 in the second direction D2. The clutch housing 30 holds theplurality of input-side rotating plates 20.

As illustrated in FIG. 1 , an input gear 35 is disposed on the bottomwall 31 of the clutch housing 30. The input gear 35 is fixed to thebottom wall 31 by a rivet 35B through a torque damper 35A. The inputgear 35 meshes with a driving gear (not shown) that rotates byrotational driving of the input shaft of the engine. The input gear 35is rotationally driven together with the clutch housing 30,independently of the output shaft 15.

The input-side rotating plates 20 is rotationally driven by rotationaldriving of the input shaft. As illustrated in FIG. 1 , the input-siderotating plates 20 are held on the inner peripheral surface of the sidewall 33 of the clutch housing 30. The input-side rotating plates 20 areheld in the clutch housing 30 by spline fitting. The input-side rotatingplates 20 are displaceable along the axial direction of the clutchhousing 30. The input-side rotating plates 20 are rotatable togetherwith the clutch housing 30.

The input-side rotating plates 20 are pushed against the output-siderotating plates 22. The input-side rotating plates 20 are ring-shapedflat plates. Each of the input-side rotating plates 20 is shaped bypunching a thin plate of a steel plate cold commercial (SPCC) materialinto a ring shape. Friction members (not shown) of a plurality of papersheets are attached to the front and back surfaces of the input-siderotating plates 20. A groove with a depth of several micrometers toseveral tens of micrometers is formed between the friction members tohold clutch oil.

As illustrated in FIG. 1 , the clutch center 40 is housed in the clutchhousing 30. The clutch center 40 and the clutch housing 30 areconcentrically disposed. The clutch center 40 includes a cylindricalbody 42 and a flange 68 extending radially outward from the outer edgeof the body 42. The clutch center 40 holds the plurality of output-siderotating plates 22 arranged alternately with the input-side rotatingplates 20 in the directions D. The clutch center 40 is rotationallydriven together with the output shaft 15.

As illustrated in FIG. 2 , the body 42 includes a ring-shaped base wall43, an outer peripheral wall 45 located radially outward of the basewall 43 and extending in the second direction D2, an output shaftholding portion 50 disposed at the center of the base wall 43, aplurality of center-side cam portions 60 connected to the base wall 43and the outer peripheral wall 45, and a center-side fitting portion 58.

The output shaft holding portion 50 has a cylindrical shape. The outputshaft holding portion 50 has an insertion hole 51 in which the outputshaft 15 is inserted and spline-fitted. The insertion hole 51 penetratesthe base wall 43. An inner peripheral surface 50A of the output shaftholding portion 50 defining the insertion hole 51 includes a pluralityof spline grooves formed along the axial direction. The output shaft 15is coupled to the output shaft holding portion 50.

As illustrated in FIG. 2 , the outer peripheral wall 45 of the clutchcenter 40 is disposed radially outward of the output shaft holdingportion 50. The outer peripheral wall 45 is located radially outward ofthe center-side cam portions 60. The outer peripheral surface 45A of theouter peripheral wall 45 includes a spline fitting portion 46. Thespline fitting portion 46 includes a plurality of center-side fittingteeth 47 extending in the axial directions of the clutch center 40 alongthe outer peripheral surface 45A of the outer peripheral wall 45, aplurality of spline grooves 48 each formed between adjacent ones of thecenter-side fitting teeth 47 and extending in the axial directions ofthe clutch center 40, and oil flow holes 49. The center-side fittingteeth 47 hold the output-side rotating plates 22. The plurality ofcenter-side fitting teeth 47 are arranged in the circumferentialdirections S. The plurality of center-side fitting teeth 47 are arrangedat regular or substantially regular intervals in the circumferentialdirections S. The plurality of center-side fitting teeth 47 have thesame or substantially the same shape. The center-side fitting teeth 47project radially outward from the outer peripheral surface 45A of theouter peripheral wall 45. The oil flow holes 49 penetrate the outerperipheral wall 45 along the radial directions. Each of the oil flowholes 49 is formed between adjacent ones of the center-side fittingteeth 47. That is, the oil flow holes 49 are formed in the splinegrooves 48. The oil flow holes 49 are formed at the sides of thecenter-side cam portions 60. More specifically, the discharge holes 49are formed at the sides of the center-side slipper cam surfaces 60S ofthe center-side cam portions 60. The oil flow holes 49 are located aheadof the center-side slipper cam surfaces 60S in the secondcircumferential direction S2. The oil flow holes 49 are located ahead ofbosses 54 described later in the first circumferential direction S1. Inthis preferred embodiment, two oil flow holes 49 are formed in each ofthree portions of the peripheral wall 45 in the circumferentialdirections S. The oil flow holes 49 are arranged at regular orsubstantially regular intervals in the circumferential directions S. Theoil flow holes 49 cause the inside and outside of the clutch center 40to communicate with each other. The oil flow holes 49 allow clutch oilthat has flowed from the output shaft 15 into the clutch center 40 to bedischarged to the outside of the clutch center 40.

The output-side rotating plates 22 are held by the spline fittingportion 46 of the clutch center 40 and the pressure plate 70. A portionof the output-side rotating plates 22 is held by the center-side fittingteeth 47 of the clutch center 40 and the spline grooves 48 by splinefitting. Another portion of the output-side rotating plates 22 is heldby pressure-side fitting teeth 77 (see FIG. 6 , described later) of thepressure plate 70. The output-side rotating plates 22 are displaceablealong the axial directions of the clutch center 40. The output-siderotating plates 22 are rotatable together with the clutch center 40.

The output-side rotating plates 22 are pushed against the input-siderotating plates 20. The output-side rotating plates 22 are ring-shapedflat plates. Each of the output-side rotating plates 22 is shaped bypunching a thin plate of an SPCC material into a ring shape. The frontand back surfaces of the output-side rotating plates 22 have grooveswith depths of several micrometers to several tens of micrometers, forexample, to hold clutch oil. The front and back surfaces of theoutput-side rotating plates 22 are subjected to a surface hardeningtreatment to enhance abrasion resistance. The friction members providedon the input-side rotating plates 20 may be provided on the output-siderotating plates 22 instead of the input-side rotating plates 20, or maybe provided on both the input-side rotating plates 20 and theoutput-side rotating plates 22.

Each of the center-side cam portions 60 is formed in a trapezoidal shapeincluding a cam surface of a slope defining an assist & slipper(registered trademark) mechanism that generates an assist torque as aforce of increasing a pressing force (contact pressure force) betweenthe input-side rotating plates 20 and the output-side rotating plates 22or a slipper torque as a force of separating the input-side rotatingplates 20 and the output-side rotating plates 22 from each other earlyand shifting these plates into a half-clutch state. The center-side camportions 60 project from the base wall 43 in the second direction D2. Asillustrated in FIG. 3 , the center-side cam portions 60 are arranged atregular or substantially regular intervals in the circumferentialdirections S of the clutch center 40. In this preferred embodiment, theclutch center 40 includes three center-side cam portions 60, but thenumber of the center-side cam portions 60 is not limited to three.

As illustrated in FIG. 3 , the center-side cam portions are locatedradially outward of the output shaft holding portion 50. Each of thecenter-side cam portions 60 includes the center-side assist cam surface60A and the center-side slipper cam surface 60S. The center-side assistcam surface 60A is configured to generate a force in a direction inwhich the pressure plate 70 approaches the clutch center 40 in order toincrease a pressing force (contact pressure force) between theinput-side rotating plates 20 and the output-side rotating plates 22 inrelative rotation to the pressure plate 70. In this preferredembodiment, when this force is generated, the position of the pressureplate 70 to the clutch center 40 does not change, and the pressure plate70 does not need to approach the clutch center 40 physically. Thepressure plate 70 may be physically displaced with respect to the clutchcenter 40. The center-side slipper cam surface 60S is configured toseparate the pressure plate 70 from the clutch center 40 in order toreduce the pressing force (contact pressure force) between theinput-side rotating plates 20 and the output-side rotating plates 22 inrelative rotation to the pressure plate 70. In the center-side camportions 60 adjacent to each other in the circumferential directions S,the center-side assist cam surface 60A of one center-side cam portion60L and the center-side slipper cam surface 60S of the other center-sidecam portion 60M are opposed to each other in the circumferentialdirections S.

As illustrated in FIG. 2 , each of the center-side cam portions 60includes a first center-side recess 62 that is recessed in the firstdirection D1 from a surface 60D2 of the center-side cam portion 60 atthe side of the second direction D2. The first center-side recess 62 islocated ahead of the center-side slipper cam surface 60S in the secondcircumferential direction S2. As illustrated in FIG. 5 , when seen inthe axial directions (i.e., directions D) of the output shaft 15, atleast a portion of the first center-side recess 62 overlaps with thecenter-side assist cam surface 60A. As illustrated in FIG. 14 , whenseen in the axial direction of the output shaft 15 (i.e., directions D),for example, at least about one half of the first center-side recess 62overlaps with the center-side assist cam surface 60A with respect to thecircumferential directions S. When seen in the axial direction of theoutput shaft 15 (i.e., directions D), for example, at least about onehalf of the first center-side recess 62 overlaps with a center-side camhole 43H with respect to the circumferential directions S. The firstcenter-side recess 62 includes a first center-side slope 63 parallel orsubstantially parallel to the center-side assist cam surface 60A. Thefirst center-side slope 63 tilts to gradually approach the seconddirection D2 in the second circumferential direction S2.

As illustrated in FIG. 4 , each of the center-side cam portions 60includes a second center-side recess 64 that is recessed in the seconddirection D2 from a surface 60D1 of the center-side cam portion 60 atthe side of the first direction D1. The second center-side recess 64 islocated ahead of the center-side assist cam surface 60A in the firstcircumferential direction S1. As illustrated in FIG. 3 , when seen inthe axial direction of the output shaft 15 (i.e., directions D), atleast a portion of the second center-side recess 64 overlaps with thecenter-side slipper cam surface 60S. As illustrated in FIG. 14 , thesecond center-side recess 64 includes a second center-side slope 65parallel or substantially parallel to the center-side slipper camsurface 60S. The second center-side slope 65 tilts to gradually approachthe first direction D1 in the first circumferential direction S1.

As illustrated in FIG. 14 , an end 62A of the first center-side recess62 in the first direction D1 is located ahead, in the first directionD1, of an end 64A of the second center-side recess 64 in the seconddirection D2. The end 62A of the first center-side recess 62 in thefirst direction D1 may be located ahead, in the second direction D2, ofthe end 64A of the second center-side recess 64 in the second directionD2. A length L1 of the first center-side recess 62 in the directions Dis shorter than a length L2 of the second center-side recess 64 in thedirections D. A length LS1 of the first center-side recess 62 in thecircumferential directions S is shorter than a length LS2 of the secondcenter-side recess 64 in the circumferential directions S. Asillustrated in FIG. 3 , when seen in the axial direction of the outputshaft 15 (i.e., directions D), the first center-side recess 62 and thesecond center-side recess 64 do not overlap with each other.

As illustrated in FIG. 3 , the clutch center 40 includes an oil passage53 formed through the peripheral wall 45. The oil passage 53 is formedin spline grooves 48 to penetrate the peripheral wall 45. The oilpassage 53 is formed between adjacent ones of the center-side fittingteeth 47. One end of the oil passage 53 is open radially inward andcommunicates with the second center-side recess 64. The other end of theoil passage 53 is open radially outward and communicates with theoutside of the peripheral wall 45. The oil passage 53 guides clutch oilthat has flowed out of the output shaft 15 into the second center-siderecess 64 from the side of the clutch center 40 in the first directionD1 to the outside of the clutch center 40 (radially outward of theclutch center 40) through the spline grooves 48. Accordingly, clutch oilis supplied through the oil passage 53 to the output-side rotatingplates 22 and the input-side rotating plates 20 held by the center-sidefitting teeth 47.

As illustrated in FIG. 2 , the clutch center 40 includes the pluralityof (for example, three in this preferred embodiment) bosses 54. Thebosses 54 support the pressure plate 70. The plurality of bosses 54 arearranged at regular or substantially regular intervals in thecircumferential directions S. Each of the bosses 54 has a cylindricalshape. The bosses 54 are located radially outward of the output shaftholding portion 50. The bosses 54 extend toward the pressure plate 70(i.e., in the second direction D2). The bosses 54 are disposed on thebase wall 43. The bosses 54 have screw holes 54H in which bolts 28 (seeFIG. 1 ) are inserted. The screw holes 54H extend in the axialdirections of the clutch center 40.

As illustrated in FIG. 2 , the center-side fitting portion 58 is locatedradially outward of the output shaft holding portion 50. The center-sidefitting portion 58 is located radially outward of the center-side camportions 60. The center-side fitting portion 58 is disposed ahead of thecenter-side cam portions 60 in the second direction D2. The center-sidefitting portion 58 is formed on the inner peripheral surface of theouter peripheral wall 45. The center-side fitting portion 58 is slidablyfitted onto a pressure-side fitting portion 88 (see FIG. 6 ) describedlater. The inner diameter of the center-side fitting portion 58 has afitting tolerance allowing distribution of clutch oil flowing out of adistal end 15T of the output shaft 15 to the pressure-side fittingportion 88. That is, a gap is formed between the center-side fittingportion 58 and the pressure-side fitting portion 88 described later. Inthis preferred embodiment, for example, the center-side fitting portion58 has an inner diameter larger than the outer diameter of thepressure-side fitting portion 88 by about 0.1 mm. This dimensionaltolerance between the inner diameter of the center-side fitting portion58 and the outer diameter of the pressure-side fitting portion 88 isappropriately set in accordance with the amount of clutch oil intendedto be distributed, and is, for example, about 0.1 mm or more and about0.5 mm or less.

As illustrated in FIGS. 2 and 3 , the clutch center 40 includes thecenter-side cam holes 43H penetrating a portion of the base wall 43. Thecenter-side cam holes 43H extend from portions on the side of the outputshaft holding portion 50 to the outer peripheral wall 45. Thecenter-side cam holes 43H are formed through the base wall 43 betweenadjacent ones of the center-side cam portion 60. Each center-side camhole 43H is formed between the center-side assist cam surface 60A of thecenter-side cam portion 60 and the boss 54. When seen in the axialdirection of the clutch center 40, the center-side assist cam surface60A overlaps with a portion of the center-side cam hole 43H.

As illustrated in FIG. 1 , the pressure plate 70 is movable toward oraway from the clutch center 40 and rotatable relative to the clutchcenter 40. The pressure plate 70 is configured to press the input-siderotating plates 20 and the output-side rotating plates 22. The pressureplate 70 is disposed coaxially with the clutch center 40 and the clutchhousing 30. The pressure plate 70 includes a body 72, and a flange 98connected to the outer edge of the body 72 on the side of the seconddirection D2 and extending radially outward. The body 72 projects aheadof the flange 98 in the first direction D1. The flange 98 is locatedradially outward of a cylindrical portion 80 (see FIG. 6 ) describedlater. The pressure plate 70 holds the plurality of output-side rotatingplates 22 arranged alternately with the input-side rotating plates 20.The flange 98 is configured to press the input-side rotating plates 20and the output-side rotating plates 22.

As illustrated in FIG. 6 , the body 72 includes the cylindrical portion80, the plurality of pressure-side cam portions 90, the pressure-sidefitting portion 88, and a spring housing portion 84 (see also FIG. 8 ).

The cylindrical portion 80 has a cylindrical shape. The cylindricalportion 80 is integrally formed with the pressure-side cam portions 90.The cylindrical portion 80 houses the distal end 15T of the output shaft15 (see FIG. 1 ). The cylindrical portion 80 houses the release bearing18 (see FIG. 1 ). The cylindrical portion 80 receives a pressing forcefrom the push member 16B. The cylindrical portion 80 receives clutch oilthat has flowed out from the distal end 15T of the output shaft 15.

Each of the pressure-side cam portions 90 is formed in a trapezoidalshape having a cam surface of a slope constituting an assist & slipper(registered trademark) mechanism that slides on the center-side camportions 60 and generates an assist torque or a slipper torque. Thepressure-side cam portions 90 project from the flange 98 in the firstdirection D1. As illustrated in FIG. 7 , the pressure-side cam portions90 are arranged at regular or substantially regular intervals in thecircumferential directions S of the pressure plate 70. In this preferredembodiment, the pressure plate 70 includes three pressure-side camportions 90, but the number of the pressure-side cam portions 90 is notlimited to three.

As illustrated in FIG. 7 , the pressure-side cam portion 90 is locatedradially outward of the cylindrical portion 80. Each of thepressure-side cam portions 90 includes a pressure-side assist camsurface 90A (see also FIG. 9 ) and a pressure-side slipper cam surface90S. The pressure-side assist cam surface 90A can be brought intocontact with the center-side assist cam surface 60A. The pressure-sideassist cam surface 90A is configured to generate a force in a directionin which the pressure plate 70 approaches the clutch center 40 in orderto increase a pressing force (contact pressure force) between theinput-side rotating plates 20 and the output-side rotating plates 22 inrelative rotation to the clutch center 40. The pressure-side slipper camsurface 90S can be brought into contact with the center-side slipper camsurface 60S. The pressure-side slipper cam surface 90S is configured toseparate the pressure plate 70 from the clutch center 40 in order toreduce a pressing force (contact pressure force) between the input-siderotating plates 20 and the output-side rotating plates 22 in relativerotation to the clutch center 40. In the pressure-side cam portions 90adjacent to each other in the circumferential directions S, thepressure-side assist cam surface 90A of one pressure-side cam portion90L and the pressure-side slipper cam surface 90S of the otherpressure-side cam portion 90M are opposed to each other in thecircumferential directions S.

As illustrated in FIG. 6 , the pressure-side cam portion 90 includes afirst pressure-side recess 92 that is recessed in the second directionD2 from a surface 90D1 of the pressure-side cam portion 90 at the sideof the first direction D1. The first pressure-side recess 92 is locatedahead of the pressure-side slipper cam surface 90S in the firstcircumferential direction S1. As illustrated in FIG. 9 , when seen inthe axial direction of the output shaft 15 (i.e., directions D), atleast a portion of the first pressure-side recess 92 overlaps with thepressure-side assist cam surface 90A. As illustrated in FIG. 15 , thefirst pressure-side recess 92 includes a first pressure-side slope 93parallel or substantially parallel to the pressure-side assist camsurface 90A. The first pressure-side slope 93 tilts to graduallyapproach the first direction D1 in the first circumferential directionS1.

As illustrated in FIG. 8 , the pressure-side cam portion 90 includes asecond pressure-side recess 94 that is recessed in the first directionD1 from a surface 90D2 of the pressure-side cam portion 90 at the sideof the second direction D2. The second pressure-side recess 94 islocated ahead of the pressure-side assist cam surface 90A in the secondcircumferential direction S2. As illustrated in FIG. 7 , when seen inthe axial direction of the output shaft 15 (i.e., directions D), atleast a portion of the second pressure-side recess 94 overlaps with thepressure-side slipper cam surface 90S. As illustrated in FIG. 15 , thesecond pressure-side recess 94 includes a second pressure-side slope 95parallel or substantially parallel to the pressure-side slipper camsurface 90S. The second pressure-side slope 95 tilts to graduallyapproach the second direction D2 in the second circumferential directionS2. As illustrated in FIG. 10 , an end 94A of the second pressure-siderecess 94 in the first direction D1 is located ahead, in the firstdirection D1, of an end 88A of the pressure-side fitting portion 88 inthe first direction D1.

As illustrated in FIG. 15 , an end 92A of the first pressure-side recess92 in the second direction D2 is located ahead, in the first directionD1, of the end 94A of the second pressure-side recess 94 in the firstdirection D1. The end 92A of the first pressure-side recess 92 in thesecond direction D2 may be located ahead, in the second direction D2, ofthe end 94A of the second pressure-side recess 94 in the first directionD1. As illustrated in FIG. 3 , when seen in the axial direction of theoutput shaft 15 (i.e., directions D), the first pressure-side recess 92and the second pressure-side recess 94 do not overlap with each other.

As illustrated in FIG. 11 , when seen in the axial direction of theoutput shaft 15 (i.e., directions D, the first direction D1 in thispreferred embodiment), the second pressure-side recess 94 of thepressure plate 70 and the first center-side recess 62 of the clutchcenter 40 do not overlap with each other. When seen in the axialdirection of the output shaft 15 (i.e., directions D, the firstdirection D1 in this preferred embodiment), at least a portion of thefirst center-side recess 62 of the clutch center 40 overlaps with thepressure-side cam hole 73H of the pressure plate 70. That is, the firstcenter-side recess 62 is exposed to the outside through thepressure-side cam hole 73H. As illustrated in FIG. 12 , when seen in theaxial direction of the output shaft 15 (i.e., directions D, the seconddirection D2 in this preferred embodiment), the first pressure-siderecess 92 of the pressure plate 70 does not overlap with the secondcenter-side recess 64 of the clutch center 40. When seen in the axialdirection of the output shaft 15 (i.e., directions D, the seconddirection D2 in this preferred embodiment), at least a portion of thefirst pressure-side recess 92 of the pressure plate 70 overlaps with thecenter-side cam hole 43H of the clutch center 40. That is, the firstpressure-side recess 92 is exposed to the outside through thecenter-side cam hole 43H.

Advantages of the center-side cam portions 60 and the pressure-side camportions 90 will now be described. When the rotation speed of the engineincreases so that a rotation driving force input to the input gear 35and the clutch housing 30 is thereby allowed to be transferred to theoutput shaft 15 through the clutch center 40, a rotation force in thefirst circumferential direction S1 is applied to the pressure plate 70,as illustrated in FIG. 13A. Thus, with the effects of the center-sideassist cam surface 60A and the pressure-side assist cam surface 90A, aforce in first direction D1 is generated in the pressure plate 70.Accordingly, a contact pressure force between the input-side rotatingplates 20 and the output-side rotating plates 22 increases. FIG. 13Adoes not show the center-side recess 62, for example.

On the other hand, when the rotation speed of the output shaft 15exceeds the rotation speed of the input gear 35 and the clutch housing30 and a back torque is generated, a rotation force in the firstcircumferential direction S1 is applied to the clutch center 40, asillustrated in FIG. 13B. Thus, with the effects of the center-sideslipper cam surface 60S and the pressure-side slipper cam surface 90S,the pressure plate 70 moves in the second direction D2 and releases acontact pressure force between the input-side rotating plates 20 and theoutput-side rotating plates 22. In this manner, it is possible to avoidproblems in the engine and the transmission caused by the back torque.FIG. 13B does not show the first center-side recess 62, for example.

As illustrated in FIG. 6 , the pressure-side fitting portion 88 islocated radially outside of the pressure-side cam portions 90. Thepressure-side fitting portion 88 is located ahead of the pressure-sidecam portions 90 in the second direction D2. The pressure-side fittingportion 88 is configured to slidably fit in the center-side fittingportion 58 (see FIG. 2 ).

As illustrated in FIGS. 6 and 7 , the pressure plate 70 includespressure-side cam holes 73H penetrating the body 72 and a portion of theflange 98. The pressure-side cam holes 73H are located radially outwardof the cylindrical portion 80. The pressure-side cam holes 73H extendfrom portions on the side of the cylindrical portion 80 to the radiallyoutside of the pressure-side fitting portion 88. The pressure-side camholes 73H are formed through the body 72 between adjacent ones of thepressure-side cam portions 90. Each of the pressure-side cam holes 73His formed between the pressure-side assist cam surface 90A and thepressure-side slipper cam surface 90S of adjacent ones of thepressure-side cam portions 90. As illustrated in FIGS. 7 and 9 , whenseen in the axial direction of the pressure plate 70, the pressure-sideassist cam surface 90A overlaps with portions of the pressure-side camholes 73H.

As illustrated in FIG. 6 , the pressure plate 70 includes the pluralityof pressure-side fitting teeth 77 arranged on the flange 98. Thepressure-side fitting teeth 77 hold the output-side rotating plates 22.The pressure-side fitting teeth 77 project from the flange 98 in thefirst direction D1. The pressure-side fitting teeth 77 are locatedradially outward of the cylindrical portion 80. The pressure-sidefitting teeth 77 are located radially outward of the pressure-side camportions 90. The pressure-side fitting teeth 77 are located radiallyoutward of the pressure-side fitting portion 88. The plurality ofpressure-side fitting teeth 77 are arranged in the circumferentialdirections S. The plurality of pressure-side fitting teeth 77 arearranged at regular or substantially regular intervals in thecircumferential directions S. In this preferred embodiment, since aportion of the pressure-side fitting teeth 77 has been removed, theinterval of this portion is enlarged, but the other adjacentpressure-side fitting teeth 77 are arranged at regular or substantiallyregular intervals.

As illustrated in FIGS. 8 and 9 , the spring housing portions 84 areformed in the pressure-side cam portions 90. The spring housing portion84 is located between the first pressure-side recess 92 and the secondpressure-side recess 94. The spring housing portions 84 are recessedfrom the second direction D2 to the first direction D1. Each of thespring housing portions 84 has an oval shape. The spring housingportions 84 house pressure springs 25 (see FIG. 1 ). The spring housingportions 84 include the insertion holes 84H which penetrate the springhousing portions 84 and in which the bosses 54 (see FIG. 2 ) areinserted. That is, the insertion holes 84H penetrate the pressure-sidecam portions 90. Each of the insertion holes 84H has an oval shape.

As illustrated in FIG. 1 , the pressure springs 25 are housed in thespring housing portions 84. The pressure springs 25 are held by thebosses 54 inserted in the insertion holes 84H of the spring housingportions 84. The pressure springs 25 bias the pressure plate 70 towardthe clutch center 40 (i.e., in the first direction D1). The pressuresprings 25 are, for example, coil springs obtained by helically windingspring steel.

FIGS. 11 and 12 are plan views each illustrating a state where theclutch center 40 and the pressure plate 70 are combined. In the statesillustrated in FIGS. 11 and 12 , the pressure-side assist cam surface90A and the center-side assist cam surface 60A do not contact eachother, and the pressure-side slipper cam surface 90S and the center-sideslipper cam surface 60S do not contact each other. At this time, thepressure plate 70 is closest to the clutch center 40.

As illustrated in FIG. 1 , the stopper plate 100 can contact thepressure plate 70. The stopper plate 100 reduces or prevents separationof the pressure plate 70 from the clutch center by a predetermineddistance or more in the second direction D2. The stopper plate 100 isfixed to the bosses 54 of the clutch center 40 with the bolts 28. Thepressure plate 70 is fixed by fastening the bolts 28 to the bosses 54through the stopper plate 100 with the bosses 54 and the pressuresprings 25 of the clutch center 40 disposed in the spring housingportions 84. The stopper plate 100 is substantially triangular in planview.

When the pressure plate 70 is brought into contact with the stopperplate 100, the contact area between the pressure-side slipper camsurface 90S and the center-side slipper cam surface is about 50% or moreand about 90% or less of the area of the pressure-side slipper camsurface 90S and about 50% or more and about 90% or less of the area ofthe center-side slipper cam surface 60S, for example. When the pressureplate 70 is brought into contact with the stopper plate 100, thepressure springs 25 are separated from the side walls of the springhousing portions 84. That is, the pressure springs 25 are not sandwichedbetween the bosses 54 and the spring housing portions 84, andapplication of excessive stress to the bosses 54 is reduced orprevented.

The clutch device 10 is filled with a predetermined amount of clutchoil. Clutch oil is distributed in the clutch center 40 and the pressureplate 70 through the hollow portion 15H of the output shaft 15, and thenis supplied to the input-side rotating plates 20 and the output-siderotating plates 22 through the gap between the center-side fittingportion 58 and the pressure-side fitting portion 88 and the oil flowholes 49. Clutch oil reduces or prevents absorption of heat and abrasionof the friction members. The clutch device 10 according to thispreferred embodiment is a so-called multiplate wet friction clutchdevice.

Operation of the clutch device 10 according to this preferred embodimentwill now be described. As described above, the clutch device 10 isdisposed between the engine and the transmission of the motorcycle, andallows or interrupts transfer of a rotation driving force of the engineto the transmission by driver's operation of a clutch operation lever.

In the clutch device 10, in a case where the driver of the motorcycledoes not operate the clutch operation lever, a clutch release mechanism(not shown) does not press the push rod 16A, and thus, the pressureplate 70 presses the input-side rotating plates 20 with a biasing force(elastic force) of the pressure springs 25. Accordingly, the clutchcenter 40 enters a clutch-ON state in which the input-side rotatingplates 20 and the output-side rotating plates 22 are pushed against eachother to be friction coupled, and is rotationally driven. That is, arotation driving force of the engine is transferred to the clutch center40, and the output shaft 15 is rotationally driven.

In the clutch-ON state, clutch oil distributed in the hollow portion Hof the output shaft 15 and having flowed out from the distal end 15T ofthe output shaft 15 is dropped or spattered in the cylindrical portion80 and attached to the cylindrical portion 80 (see arrow F in FIG. 1 ).The clutch oil attached to the inside of the cylindrical portion 80 isguided into the clutch center 40. Accordingly, clutch oil flows out ofthe clutch center 40 through the oil flow holes 49. Clutch oil alsoflows out of the clutch center 40 through the gap between thecenter-side fitting portion 58 and the pressure-side fitting portion 88.Then, clutch oil that has flowed out of the clutch center 40 is suppliedto the input-side rotating plates 20 and the output-side rotating plates22.

On the other hand, in the clutch device 10, when the driver of themotorcycle operates the clutch operation lever in the clutch-ON state,the clutch release mechanism (not shown) presses the push rod 16A, andthus, the pressure plate 70 is displaced in a direction away from theclutch center 40 (second direction D2) against a biasing force of thepressure springs 25. Accordingly, the clutch center 40 enters aclutch-OFF state in which friction coupling between the input-siderotating plates 20 and the output-side rotating plates 22 is canceled,and thus, rotational driving attenuates or stops. That is, a rotationdriving force of the engine is interrupted to the clutch center 40.

In the clutch-OFF state, clutch oil distributed in the hollow portion Hof the output shaft 15 and having flowed out of the distal end 15T ofthe output shaft 15 is guided into the clutch center 40 in the same orsubstantially the same manner as in the clutch-ON state. At this time,since the pressure plate 70 is separated from the clutch center 40, theamount of fitting between the pressure plate 70 and each of thecenter-side fitting portion 58 and the pressure-side fitting portion 88decreases. As a result, clutch oil in the cylindrical portion 80actively flows out of the clutch center 40, and is distributed toportions in the clutch device 10. In particular, clutch oil can beactively guided to gaps between the input-side rotating plates 20 andthe output-side rotating plates 22 separated from each other.

Then, when the driver cancels the clutch operation lever in theclutch-OFF state, pressing of the pressure plate 70 by the clutchrelease mechanism (not shown) through the push member 16B is canceled,and thus, the pressure plate 70 is displaced with a biasing force of thepressure springs 25 to a direction (first direction D1) of approachingthe clutch center 40.

As described above, in the clutch device 10 according to this preferredembodiment, at least one of the center-side cam portions 60 includes atleast one of the first center-side recess 62 that is recessed in thefirst direction D1 from the surface 60D2 of the center-side cam portion60 at the side of the second direction D2 or the second center-siderecess 64 that is recessed in the second direction D2 form the surface60D1 of the center-side cam portion 60 in the first direction D1. Inthis manner, since at least one of the center-side cam portions 60includes at least one of the first center-side recess 62 or the secondcenter-side recess 64, the center-side cam portions 60 are morelightweight than those not including these recesses. Since the clutchdevice 10 includes the more lightweight clutch center 40, weightreduction of the entire clutch device 10 is achieved.

In the clutch device 10 according to this preferred embodiment, at leastone of the center-side cam portions 60 includes the first center-siderecess 62 and the second center-side recess 64. In this configuration,the weight of the center-side cam portions 60 is further reduced.

In the clutch device 10 according to this preferred embodiment, the end62A of the first center-side recess 62 in the first direction D1 islocated ahead, in the first direction D1, of the end 64A of the secondcenter-side recess 64 in the second direction D2. In this configuration,the weight of the center-side cam portions 60 is further reduced.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),at least a portion of the first center-side recess 62 overlaps with thecenter-side assist cam surface 60A. In this configuration, since aportion including the center-side assist cam surface 60A can be maderelatively thin, accurate shaping is obtained in fabrication, andsurface properties such as surface roughness of the center-side assistcam surface 60A is enhanced.

In the clutch device 10 according to this preferred embodiment, thefirst center-side recess 62 includes the first center-side slope 63parallel or substantially parallel to the center-side assist cam surface60A. In this configuration, the thickness of a portion including thecenter-side assist cam surface 60A can be made substantially uniform,and thus, performance of the center-side assist cam surface 60A isenhanced.

In the clutch device 10 according to this preferred embodiment, theclutch center 40 is configured to rotate in the first circumferentialdirection S1 that is a direction from the center-side assist cam surface60A of one center-side cam portion 60 to the center-side slipper camsurface 60S, and the first center-side slope 63 tilts to graduallyapproach the second direction D2 in the second circumferential directionS2. In this configuration, even in a case where clutch oil isaccumulated in the first center-side recess 62, clutch oil accumulatedin the first center-side recess 62 flows out in the secondcircumferential direction S2 along the first center-side slope 63.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),at least a portion of the second center-side recess 64 overlaps with thecenter-side slipper cam surface 60S. In this configuration, since aportion including the center-side slipper cam surface 60S can be maderelatively thin, accurate shaping is obtained in fabrication, andsurface properties such as surface roughness of the center-side slippercam surface 60S is enhanced.

In the clutch device 10 according to this preferred embodiment, thesecond center-side recess 64 includes the second center-side slope 65parallel or substantially parallel to the center-side slipper camsurface 60S. In this configuration, the thickness of a portion includingthe center-side slipper cam surface 60S can be made substantiallyuniform, and thus, performance of the center-side slipper cam surface60S is enhanced.

In the clutch device 10 according to this preferred embodiment, theclutch center 40 includes the peripheral wall 45 located radiallyoutward of the center-side cam portions 60, and the oil passage 53penetrating the peripheral wall 45 and having one end open radiallyinward and communicate with the second center-side recess 64 and theother end open radially outward and communicate with the outside of theperipheral wall 45. In this configuration, clutch oil that has flowedout of the output shaft 15 into the second center-side recess 64 fromthe side of the clutch center 40 in the first direction D1 can besupplied to the output-side rotating plates 22 and the input-siderotating plates 20 through the oil passage 53.

In the clutch device 10 according to this preferred embodiment, the oilpassage 53 is formed in the spline grooves 48 to penetrate theperipheral wall 45. In this configuration, since clutch oil flows alongthe spline grooves, clutch oil can be supplied to the output-siderotating plates 22 and the input-side rotating plates 20 in a balancedmanner.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),the first center-side recess 62 and the second center-side recess 64 donot overlap each other. In this configuration, even when the depth ofthe first center-side recess 62 and the depth of the second center-siderecess 64 in the axial direction of the output shaft 15 are increased,these recesses do not interfere with each other, and thus, the weight ofthe center-side cams portion 60 can be further reduced by relativelyincreasing the depths of the first center-side recess 62 and the secondcenter-side recess 64.

In the clutch device 10 according to this preferred embodiment, at leastone of the pressure-side cam portions 90 includes at least one of thefirst pressure-side recess 92 that is recessed in the second directionD2 from the surface 90D1 of the pressure-side cam portion 90 at the sideof the first direction D1 or the second pressure-side recess 94 that isrecessed in the first direction D1 from the surface 90DS of thepressure-side cam portion 90 at the side of the second direction D2. Inthis manner, since at least one of the pressure-side cam portion 90includes at least one of the first pressure-side recess 92 or the secondpressure-side recess 94, the pressure-side cam portion 90 is morelightweight than those not including these recesses. Since the clutchdevice 10 includes the more lightweight pressure plate 70, weightreduction of the entire clutch device 10 is achieved.

In the clutch device 10 according to this preferred embodiment, at leastone of the pressure-side cam portions 90 includes the firstpressure-side recess 92 and the second pressure-side recess 94. In thisconfiguration, the weight of the pressure-side cam portions 90 isfurther reduced.

In the clutch device 10 according to this preferred embodiment, thepressure plate 70 includes the spring housing portion 84 recessed in thepressure-side cam portion 90 from the second direction D2 to the firstdirection D1 and housing the pressure spring 25 that biases the pressureplate 70 in the first direction D1, and the spring housing portion 84 islocated between the first pressure-side recess 92 and the secondpressure-side recess 94. In this configuration, the weight of thepressure-side cam portions 90 is further reduced.

In the clutch device 10 according to this preferred embodiment, the end92A of the first pressure-side recess 92 in the second direction D2 maybe located ahead, in the second direction D2, of the end 94A of thesecond pressure-side recess 94 in the first direction D1. In thisconfiguration, the weight of the pressure-side cam portions 90 isfurther reduced.

In the clutch device 10 according to this preferred embodiment, theclutch center 40 includes the output shaft holding portion 50 to whichthe output shaft 15 is coupled, and the center-side fitting portion 58located radially outward of the output shaft holding portion 50, thepressure plate 70 includes the pressure-side fitting portion 88 locatedradially outward of the pressure-side cam portions 90 and slidablyfitted in the center-side fitting portion 58, and the end 94A of thesecond pressure-side recess 94 in the first direction D1 is locatedahead, in the first direction D1, of the end 88A of the pressure-sidefitting portion 88 in the first direction D1. In this configuration, theweight of the pressure-side cam portions 90 is further reduced.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),at least a portion of the first pressure-side recess 92 overlaps withthe pressure-side assist cam surface 90A. In this configuration, since aportion including the pressure-side assist cam surface 90A can be maderelatively thin, accurate shaping is obtained in fabrication, andsurface properties such as surface roughness of the pressure-side assistcam surface 90A is enhanced.

In the clutch device 10 according to this preferred embodiment, thefirst pressure-side recess 92 includes the first pressure-side slope 93parallel or substantially parallel to the pressure-side assist camsurface 90A. In this configuration, the thickness of a portion includingthe pressure-side assist cam surface 90A can be made substantiallyuniform, and thus, performance of the pressure-side assist cam surface90A is enhanced.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),at least a portion of the second pressure-side recess 94 overlaps withthe pressure-side slipper cam surface 90S. In this configuration, sincea portion including the pressure-side slipper cam surface 90S can bemade relatively thin, accurate shaping is obtained in fabrication, andsurface properties such as surface roughness of the pressure-sideslipper cam surface 90S is enhanced.

In the clutch device 10 according to this preferred embodiment, thesecond pressure-side recess 94 includes the second pressure-side slope95 parallel or substantially parallel to the pressure-side slipper camsurface 90S. In this configuration, the thickness of a portion includingthe pressure-side slipper cam surface 90S can be made substantiallyuniform, and thus, performance of the pressure-side slipper cam surface90S is enhanced.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),the first pressure-side recess 92 and the second pressure-side recess 94do not overlap with each other. In this configuration, even when thedepth of the first pressure-side recess 92 and the depth of the secondpressure-side recess 94 in the axial direction of the output shaft 15are increased, these recesses do not interfere with each other, andthus, the weight of the pressure-side cam portions 90 can be furtherreduced by relatively increasing the depths of the first pressure-siderecess 92 and the second pressure-side recess 94.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),the second pressure-side recess 94 of the pressure plate 70 and thefirst center-side recess 62 of the clutch center 40 do not overlap witheach other. In this configuration, clutch oil spattered from the seconddirection D2 toward the pressure plate 70 easily flows into the secondpressure-side recess 94 and the first center-side recess 62. Clutch oilthat has flowed into the second pressure-side recesses 94 and the firstcenter-side recesses 62 flows out of the second pressure-side recesses94 and the first center-side recesses 62 upon a shift of rotation of theengine, for example, and is supplied to the pressure-side assist camsurfaces 90A of the pressure-side cam portions 90, the center-sideassist cam surfaces 60A of the center-side cam portions 60, and otherportions. Accordingly, the pressure-side assist cam surfaces 90A, thecenter-side assist cam surfaces 60A, and other portions can be smoothlylubricated.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),at least a portion of the first center-side recess 62 overlaps with thepressure-side cam hole 73H. In this configuration, clutch oil spatteredfrom the second direction D2 toward the pressure plate 70 easily flowsinto the first center-side recess 62 through the pressure-side cam hole73H. Clutch oil that has flowed into the first center-side recesses 62flows out of the first center-side recesses 62 upon a shift of rotationof the engine, for example, and is supplied to the pressure-side assistcam surfaces 90A of the pressure-side cam portions 90, the center-sideassist cam surfaces 60A of the center-side cam portions 60, and otherportions. Accordingly, the pressure-side assist cam surfaces 90A, thecenter-side assist cam surfaces 60A, and other portions can be smoothlylubricated.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),the first pressure-side recess 92 of the pressure plate 70 and thesecond center-side recess 64 of the clutch center 40 do not overlap witheach other. In this configuration, clutch oil spattered from the firstdirection D1 toward the clutch center 40 easily flows into the firstpressure-side recess 92 and the second center-side recess 64. Clutch oilthat has flowed into the first pressure-side recesses 92 and the secondcenter-side recesses 64 flows out of the first pressure-side recesses 92and the second center-side recesses 64 upon a shift of rotation of theengine, for example, and is supplied to the pressure-side assist camsurfaces 90A of the pressure-side cam portions 90, the center-sideassist cam surfaces 60A of the center-side cam portions 60, and otherportions. Accordingly, the pressure-side assist cam surfaces 90A, thecenter-side assist cam surfaces 60A, and other portions can be smoothlylubricated.

In the clutch device 10 according to this preferred embodiment, whenseen in the axial direction of the output shaft 15 (i.e., directions D),at least a portion of the first pressure-side recess 92 overlaps withthe center-side cam hole 43H. In this configuration, clutch oilspattered from the first direction D1 toward the clutch center 40 easilyflows into the first pressure-side recess 92 through the center-side camhole 43H. Clutch oil that has flowed into the first pressure-siderecesses 92 flows out of the first pressure-side recesses 92 upon ashift of rotation of the engine, for example, and is supplied to thepressure-side assist cam surfaces 90A of the pressure-side cam portions90, the center-side assist cam surfaces 60A of the center-side camportions 60, and other portions. Accordingly, the pressure-side assistcam surfaces 90A, the center-side assist cam surfaces 60A, and otherportions can be smoothly lubricated.

Second Preferred Embodiment

FIG. 16 is a disassembled perspective view of a clutch center 240 and apressure plate 270 of a clutch device 210 according to a secondpreferred embodiment.

The clutch center 240 is housed in a clutch housing 30 (see FIG. 1 ).The clutch center 240 and the clutch housing 30 are concentricallydisposed. As illustrated in FIG. 16 , the clutch center 240 includes abody 242, and a flange 268 connected to an outer edge of the body 242 onthe side of a first direction D1 and extending radially outward. Thebody 242 projects from the flange 268 in a second direction D2. Theclutch center 240 does not hold output-side rotating plates 22. Theclutch center 240 is rotationally driven together with an output shaft15 (see FIG. 1 ).

As illustrated in FIG. 16 , the body 242 includes an output shaftholding portion 250, a plurality of center-side cam portions 60, and acenter-side fitting portion 258. The center-side cam portions 60 projectfrom the flange 268 in the second direction D2. The center-side camportions 60 are located radially outward of the output shaft holdingportion 250.

The output shaft holding portion 250 has a cylindrical shape. The outputshaft holding portion 250 has an insertion hole 251 in which the outputshaft 15 (see FIG. 1 ) is inserted and spline-fitted. The insertion hole251 penetrates the body 242. An inner peripheral surface 250A of theoutput shaft holding portion 250 defining the insertion hole 251 has aplurality of spline grooves along the axial direction. The output shaft15 is coupled to the output shaft holding portion 250.

As illustrated in FIG. 16 , the clutch center 240 includes a pluralityof (for example, three in this preferred embodiment) bosses 54. Thebosses 54 are located radially outward of the output shaft holdingportion 250. The bosses 54 are disposed on the body 242.

As illustrated in FIG. 16 , the clutch center 240 includes center-sidecam holes 243H penetrating the body 242 and a portion of the flange 268.The center-side cam holes 243H penetrate the body 242 and the flange 268in directions D. The center-side cam holes 243H are located radiallyoutward of the output shaft holding portion 250. As illustrated in FIG.17 , the center-side cam holes 243H extend from portions on the side ofthe output shaft holding portion 250 to the flange 268. Each of thecenter-side cam holes 243H is located between adjacent ones of thecenter-side cam portions 60. The center-side cam holes 243H are formedbetween the center-side assist cam surfaces 60A of the center-side camportions 60 and the bosses 54. When seen in the axial direction of theclutch center 240, the center-side assist cam surfaces 60A overlap witha portion of the center-side cam holes 243H.

As illustrated in FIG. 16 , the center-side fitting portion 258 isdisposed on the body 242. The center-side fitting portion 258 isdisposed radially outward of the center-side cam portions 60. Thecenter-side fitting portion 258 is located ahead of the center-side camportions 60 in the first direction D1. The center-side fitting portion258 is configured to slidably fit in the pressure-side fitting portion288 (see FIG. 18 ).

As illustrated in FIG. 16 , each of the center-side cam portions 60includes a first center-side recess 62 that is recessed in the firstdirection D1 from a surface 60D2 of the center-side cam portion 60 atthe side of the second direction D2. The first center-side recess 62 islocated ahead of the center-side slipper cam surface 60S in a secondcircumferential direction S2. As illustrated in FIG. 17 , when seen inthe axial directions (i.e., directions D) of the output shaft 15, atleast a portion of the first center-side recess 62 overlaps with thecenter-side assist cam surface 60A. When seen in the axial direction ofthe output shaft 15 (i.e., directions D), for example, at least aboutone half of the first center-side recess 62 overlaps with thecenter-side assist cam surface 60A with respect to circumferentialdirections S. When seen in the axial direction of the output shaft 15(i.e., directions D), for example, at least about one half of the firstcenter-side recess 62 overlaps with a center-side cam hole 243H withrespect to the circumferential directions S.

The pressure plate 270 is movable toward or away from the clutch center240 and rotatable relative to the clutch center 240. The pressure plate270 is configured to press input-side rotating plates 20 and theoutput-side rotating plates 22. The pressure plate 270 is disposedcoaxially with the clutch center 240 and the clutch housing 30. Thepressure plate 270 includes a cylindrical body 272, and a flange 298extending radially outward from the outer edge of the body 272. Thepressure plate 270 holds the plurality of output-side rotating plates 22alternately arranged with the input-side rotating plates 20 in thedirections D. In this preferred embodiment, the pressure plate 270 holdsall the output-side rotating plates 22.

As illustrated in FIG. 18 , the body 272 includes a ring-shaped basewall 273, an outer peripheral wall 275 located radially outward of thebase wall 273 and extending in the first direction D1, a cylindricalportion 280 disposed at the center of the base wall 273, a plurality ofpressure-side cam portions 90 connected to the base wall 273 and theouter peripheral wall 275, a pressure-side fitting portion 288, and aspring housing portion 84 (see FIG. 16 ). The pressure-side cam portions90 project from the body 272 in the first direction D1. Thepressure-side cam portions 90 are located radially outward of thecylindrical portion 280. The pressure-side cam portions 90 are locatedradially inward of the outer peripheral wall 275.

The cylindrical portion 280 has a cylindrical shape. The cylindricalportion 280 is formed integrally with the pressure-side cam portions 90.The cylindrical portion 280 houses a distal end 15T of the output shaft15 (see FIG. 1 ). The cylindrical portion 280 houses a release bearing18 (see FIG. 1 ). The cylindrical portion 280 receives a pressing forcefrom a push member 16B. The cylindrical portion 280 receives clutch oilthat has flowed out from the distal end 15T of the output shaft 15.

As illustrated in FIG. 18 , the outer peripheral wall 275 of thepressure plate 270 is located radially outward of the cylindricalportion 280. The outer peripheral wall 275 has a ring shape extending inthe directions D. An outer peripheral surface 275A of the outerperipheral wall 275 has a spline fitting portion 276. The spline fittingportion 276 includes a plurality of pressure-side fitting teeth 277extending in the axial direction of the pressure plate 270 along theouter peripheral surface 275A of the outer peripheral wall 275, aplurality of spline grooves 278 each formed between adjacent ones of thepressure-side fitting teeth 277 and extending in the axial direction ofthe pressure plate 270, and oil flow holes 279. The pressure-sidefitting teeth 277 hold the output-side rotating plates 22. The pluralityof pressure-side fitting teeth 277 are arranged in the circumferentialdirections S. The plurality of pressure-side fitting teeth 277 arearranged at regular or substantially regular intervals in thecircumferential directions S. The plurality of pressure-side fittingteeth 277 have the same or substantially the same shape. Thepressure-side fitting teeth 277 project radially outward from the outerperipheral surface 275A of the outer peripheral wall 275. The oil flowholes 279 penetrate the outer peripheral wall 275 in the radialdirections. Each of the oil flow holes 279 is formed between adjacentones of the pressure-side fitting teeth 277. That is, the oil flow holes279 are formed in the spline grooves 278. The oil flow holes 279 areformed at the sides of the pressure-side cam portions 90. The oil flowholes 279 are formed at the sides of pressure-side assist cam surfaces90A of the pressure-side cam portions 90. The oil flow holes 279 arelocated ahead of the pressure-side assist cam surfaces 90A in the firstcircumferential direction S1. The oil flow holes 279 are located aheadof pressure-side slipper cam surfaces 90S in the second circumferentialdirection S2. In this preferred embodiment, three oil flow holes 279 areformed in each of three portions of the peripheral wall 275 in thecircumferential directions S. The oil flow holes 279 are arranged atregular or substantially intervals in the circumferential directions S.The oil flow holes 279 cause the inside and outside of the pressureplate 270 with each other. The oil flow holes 279 allow clutch oil thathas flowed out of the output shaft 15 into the pressure plate 270 to bedischarged to the outside of the pressure plate 270. In this preferredembodiment, the oil flow holes 279 allow clutch oil flowing at an innerperipheral surface 275B of the peripheral wall 275 to be discharged tothe outside of the pressure plate 270. At least a portion of the oilflow holes 279 is located at a position facing the center-side fittingportion 258 (see FIG. 16 ).

The output-side rotating plates 22 are held by the spline fittingportion 276 of the pressure plate 270. The output-side rotating plates22 are held by the pressure-side fitting teeth 277 and the splinegrooves 278 by spline-fitting. The output-side rotating plates 22 aredisplaceable along the axial direction of the pressure plate 270. Theoutput-side rotating plates 22 are rotatable together with the pressureplate 270.

As illustrated in FIGS. 16 and 18 , the pressure plate 270 includespressure-side cam holes 273H penetrating a portion of the base wall 273.The pressure-side cam holes 273H penetrate the base wall 273 in thedirections D. The pressure-side cam holes 273H are located radiallyoutward of the cylindrical portion 80. The pressure-side cam holes 273Hextend from the sides of the cylindrical portion 80 to the outerperipheral wall 275. Each of the pressure-side cam holes 273H penetratesa portion between adjacent ones of the pressure-side cam portions 90.Each of the pressure-side cam holes 273H penetrates a portion betweenthe pressure-side assist cam surface 90A and the pressure-side slippercam surface 90S of adjacent ones of the pressure-side cam portions 90.When seen in the axial direction of the pressure plate 270, thepressure-side assist cam surfaces 90A overlap with a portion of thepressure-side cam holes 273H. Clutch oil flows into the pressure-sidecam holes 273H from the outside of the pressure plate 270.

As illustrated in FIG. 18 , the pressure-side fitting portion 288 islocated radially outward of the cylindrical portion 280. Thepressure-side fitting portion 288 is located radially outward of thepressure-side cam portions 90. The pressure-side fitting portion 288 islocated ahead of the pressure-side cam portions 90 in the firstdirection D1. The pressure-side fitting portion 288 is formed on theinner peripheral surface 275B of the peripheral wall 275. Thepressure-side fitting portion 288 is configured to slidably fit onto thecenter-side fitting portion 258 (see FIG. 16 ). A gap is formed betweenthe pressure-side fitting portion 288 and the center-side fittingportion 258.

As illustrated in FIG. 18 , each of the pressure-side cam portions 90includes a first pressure-side recess 92 that is recessed in the seconddirection D2 from a surface 90D1 of the pressure-side cam portion 90 atthe side of the first direction D1. The first pressure-side recess 92 islocated ahead of the pressure-side slipper cam surface 90S in the firstcircumferential direction S1. As illustrated in FIG. 19 , when seen inthe axial direction of the output shaft 15 (i.e., directions D), atleast a portion of the first pressure-side recess 92 overlaps with thepressure-side assist cam surface 90A.

As illustrated in FIG. 16 , the pressure-side cam portion 90 includes asecond pressure-side recess 94 that is recessed in the first directionD1 from a surface 90D2 of the pressure-side cam portion 90 at the sideof the second direction D2. The second pressure-side recess 94 islocated ahead of the pressure-side assist cam surface 90A in the secondcircumferential direction S2. When seen in the axial direction of theoutput shaft 15 (i.e., directions D), at least a portion of the secondpressure-side recess 94 overlaps with the pressure-side slipper camsurface 90S.

The foregoing description is directed to the preferred embodiments ofthe present disclosure. The preferred embodiments described above,however, are merely examples, and the present disclosure can beperformed in various modes and through various preferred embodiments.

In the first preferred embodiment described above, each of thecenter-side cam portions 60 includes the first center-side recess 62 andthe second center-side recess 64, but may include at least one of thefirst center-side recess 62 or the second center-side recess 64. In thefirst preferred embodiment, all of the center-side cam portions 60include the first center-side recess 62 and the second center-siderecess 64, but at least one of the center-side cam portions 60 mayinclude at least one of the first center-side recess 62 or the secondcenter-side recess 64. In the second preferred embodiment, each of thecenter-side cam portions 60 may include the second center-side recess64. In the second preferred embodiment, all of the center-side camportions 60 include the first center-side recess 62, but at least one ofthe center-side cam portions 60 may include at least one of the firstcenter-side recess 62 or the second center-side recess 64. In the firstpreferred embodiment and the second preferred embodiment, each of thepressure-side cam portions 90 includes the first pressure-side recess 92and the second pressure-side recess 94, but may include at least one ofthe first pressure-side recess 92 or the second pressure-side recess 94.In the first preferred embodiment and the second preferred embodiment,all of the pressure-side cam portions 90 include the first pressure-siderecess 92 and the second pressure-side recess 94, but at least one ofthe pressure-side cam portions 90 may include at least one of the firstpressure-side recess 92 or the second pressure-side recess 94.

The shapes of the first center-side recess 62, the second center-siderecess 64, the first pressure-side recess 92, and the secondpressure-side recess 94 are not specifically limited. These shapes maybe circular, oval, or rectangular, for example.

In the preferred embodiments described above, at least one of thecenter-side cam portions 60 includes the center-side assist cam surface60A and the center-side slipper cam surface 60S, but only needs toinclude at least the center-side assist cam surface 60A.

In the preferred embodiments described above, at least one of thepressure-side cam portions 90 includes the pressure-side assist camsurface 90A and the pressure-side slipper cam surface 90S, but onlyneeds to include at least the pressure-side assist cam surface 90A.

In the preferred embodiments described above, when seen in the axialdirection of the output shaft 15 (i.e., directions D), for example, atleast about one half of the first center-side recess 62 overlaps withthe center-side assist cam surface 60A with respect to thecircumferential directions S, but the present disclosure is not limitedto these preferred embodiments. For example, as illustrated in FIG. 20 ,for example, at least about one half of the first center-side recess 62of a clutch center 340 may be located closer to the center-side slippercam surface 60S than the center-side assist cam surface 60A with respectto the circumferential direction S, when seen in the axial direction ofthe output shaft 15 (i.e., directions D). In FIG. 20 , the firstcenter-side recess 62 includes the first center-side slope 63 parallelor substantially parallel to the center-side assist cam surface 60A. Thefirst center-side slope 63 tilts to gradually approach the seconddirection D2 in the second circumferential direction S2. When seen inthe axial direction of the output shaft 15 (i.e., directions D), thefirst center-side slope 63 overlaps with the center-side assist camsurface 60A. In this example, all the first center-side slopes 63overlap with the center-side assist cam surfaces 60A.

In the second preferred embodiment described above, the clutch center240 is configured not to hold the output-side rotating plates 22, butthe present disclosure is not limited to this preferred embodiment. Theclutch center 240 may include center-side fitting teeth having aconfiguration similar to that of the pressure-side fitting teeth 77 ofthe first preferred embodiment capable of holding the output-siderotating plates 22.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A clutch device to allow or interrupt transfer ofa rotation driving force of an input shaft to an output shaft, theclutch device comprising: a clutch center housed in a clutch housingholding a plurality of input-side rotating plates to be rotationallydriven together with the output shaft, the input-side rotating platesbeing operable to be rotationally driven by rotational driving of theinput shaft; and a pressure plate movable toward or away from the clutchcenter and rotatable relative to the clutch center to press theinput-side rotating plates and output-side rotating plates, theinput-side rotating plates and the output-side rotating plates beingalternately arranged; wherein the pressure plate includes: a body; and aplurality of pressure-side cam portions, assuming a direction in whichthe pressure plate approaches the clutch center is a first direction,and a direction in which the pressure plate moves away from the clutchcenter is a second direction, each of the pressure-side cam portionsprojecting from a surface of the body at a side of the first directionin the first direction, being located radially outward of the outputshaft, and including a pressure-side assist cam surface and apressure-side slipper cam surface, the pressure-side assist cam surfacebeing operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center,the pressure-side slipper cam surface being operable to cause thepressure plate to move away from the clutch center in order to reducethe pressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center;at least one of the pressure-side cam portions includes at least one ofa first pressure-side recess or a second pressure-side recess, the firstpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect tocircumferential directions and recessed in the second direction from asurface of the pressure-side cam portion at a side of the firstdirection, the second pressure-side recess being located between thepressure-side assist cam surface and the pressure-side slipper camsurface with respect to the circumferential directions and recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction; and when seen in an axial direction of theoutput shaft, at least a portion of the first pressure-side recessoverlaps with the pressure-side assist cam surface.
 2. The clutch deviceaccording to claim 1, wherein the first pressure-side recess includes afirst pressure-side slope parallel or substantially parallel to thepressure-side assist cam surface.
 3. The clutch device according toclaim 2, wherein assuming a direction from one pressure-side cam portionto another pressure-side cam portion in the pressure-side cam portionsis a first circumferential direction and a direction from the anotherpressure-side cam portion to the one pressure-side cam portion is asecond circumferential direction with respect to the circumferentialdirections, the pressure plate is operable to rotate in the firstcircumferential direction that is a direction from the pressure-sideslipper cam surface to the pressure-side assist cam surface of one ofthe pressure-side cam portions; and the first pressure-side slope tiltsto approach the first direction in the first circumferential direction.4. A clutch device to allow or interrupt transfer of a rotation drivingforce of an input shaft to an output shaft, the clutch devicecomprising: a clutch center housed in a clutch housing holding aplurality of input-side rotating plates to be rotationally driventogether with the output shaft, the input-side rotating plates beingoperable to be rotationally driven by rotational driving of the inputshaft; and a pressure plate movable toward or away from the clutchcenter and rotatable relative to the clutch center to press theinput-side rotating plates and output-side rotating plates, theinput-side rotating plates and the output-side rotating plates beingalternately arranged; wherein the pressure plate includes: a body; and aplurality of pressure-side cam portions, assuming a direction in whichthe pressure plate approaches the clutch center is a first direction,and a direction in which the pressure plate moves away from the clutchcenter is a second direction, each of the pressure-side cam portionsprojecting from a surface of the body at a side of the first directionin the first direction, being located radially outward of the outputshaft, and including a pressure-side assist cam surface and apressure-side slipper cam surface, the pressure-side assist cam surfacebeing operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center,the pressure-side slipper cam surface being operable to cause thepressure plate to move away from the clutch center in order to reducethe pressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center;at least one of the pressure-side cam portions includes at least one ofa first pressure-side recess or a second pressure-side recess, the firstpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect tocircumferential directions and recessed in the second direction from asurface of the pressure-side cam portion at a side of the firstdirection, the second pressure-side recess being located between thepressure-side assist cam surface and the pressure-side slipper camsurface with respect to the circumferential directions and recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction; and when seen in an axial direction of theoutput shaft, at least a portion of the second pressure-side recessoverlaps with the pressure-side slipper cam surface.
 5. The clutchdevice according to claim 4, wherein the second pressure-side recessincludes a second pressure-side slope parallel or substantially parallelto the pressure-side slipper cam surface.
 6. The clutch device accordingto claim 5, wherein assuming a direction from one pressure-side camportion to another pressure-side cam portion in the pressure-side camportions is a first circumferential direction and a direction from theanother pressure-side cam portion to the one pressure-side cam portionis a second circumferential direction with respect to thecircumferential directions, the pressure plate is operable to rotate inthe first circumferential direction that is a direction from thepressure-side slipper cam surface to the pressure-side assist camsurface of one of the pressure-side cam portions; and the secondpressure-side slope tilts to approach the second direction in the secondcircumferential direction.
 7. A clutch device to allow or interrupttransfer of a rotation driving force of an input shaft to an outputshaft, the clutch device comprising: a clutch center housed in a clutchhousing holding a plurality of input-side rotating plates to berotationally driven together with the output shaft, the input-siderotating plates being operable to be rotationally driven by rotationaldriving of the input shaft; and a pressure plate movable toward or awayfrom the clutch center and rotatable relative to the clutch center topress the input-side rotating plates and output-side rotating plates,the input-side rotating plates and the output-side rotating plates beingalternately arranged; wherein the pressure plate includes: a body; and aplurality of pressure-side cam portions, assuming a direction in whichthe pressure plate approaches the clutch center is a first direction,and a direction in which the pressure plate moves away from the clutchcenter is a second direction, each of the pressure-side cam portionsprojecting from a surface of the body at a side of the first directionin the first direction, being located radially outward of the outputshaft, and including a pressure-side assist cam surface and apressure-side slipper cam surface, the pressure-side assist cam surfacebeing operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center,the pressure-side slipper cam surface being operable to cause thepressure plate to move away from the clutch center in order to reducethe pressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center;at least one of the pressure-side cam portions includes at least one ofa first pressure-side recess or a second pressure-side recess, the firstpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect tocircumferential directions and recessed in the second direction from asurface of the pressure-side cam portion at a side of the firstdirection, the second pressure-side recess being located between thepressure-side assist cam surface and the pressure-side slipper camsurface with respect to the circumferential directions and recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction; and the clutch center includes: an outputshaft holding portion to which the output shaft is coupled; and aplurality of center-side cam portions located radially outward of theoutput shaft holding portion and each including a center-side assist camsurface operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the pressureplate; at least one of the center-side cam portions includes a firstcenter-side recess and a second center-side recess, the firstcenter-side recess being recessed in the first direction from a surfaceof the center-side cam portion at a side of the second direction, thesecond center-side recess being recessed in the second direction from asurface of the center-side cam portion at a side of the first direction;and when seen in an axial direction of the output shaft, the secondpressure-side recess of the pressure plate and the first center-siderecess of the clutch center do not overlap with each other.
 8. A clutchdevice to allow or interrupt transfer of a rotation driving force of aninput shaft to an output shaft, the clutch device comprising: a clutchcenter housed in a clutch housing holding a plurality of input-siderotating plates to be rotationally driven together with the outputshaft, the input-side rotating plates being operable to be rotationallydriven by rotational driving of the input shaft; and a pressure platemovable toward or away from the clutch center and rotatable relative tothe clutch center to press the input-side rotating plates andoutput-side rotating plates, the input-side rotating plates and theoutput-side rotating plates being alternately arranged; wherein thepressure plate includes: a body; a plurality of pressure-side camportions, assuming a direction in which the pressure plate approachesthe clutch center is a first direction, and a direction in which thepressure plate moves away from the clutch center is a second direction,each of the pressure-side cam portions projecting from a surface of thebody at a side of the first direction in the first direction, beinglocated radially outward of the output shaft, and including apressure-side assist cam surface and a pressure-side slipper camsurface, the pressure-side assist cam surface being operable to generatea force in a direction of causing the pressure plate to approach theclutch center in order to increase a pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the clutch center, the pressure-side slipper camsurface being operable to cause the pressure plate to move away from theclutch center in order to reduce the pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the clutch center; and a pressure-side cam holepenetrating a portion between adjacent ones of the pressure-side camportions; the clutch center includes: an output shaft holding portion towhich the output shaft is coupled; and a plurality of center-side camportions located radially outward of the output shaft holding portionand each including a center-side assist cam surface operable to generatea force in a direction of causing the pressure plate to approach theclutch center in order to increase a pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the pressure plate; at least one of thepressure-side cam portions includes at least one of a firstpressure-side recess or a second pressure-side recess, the firstpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect tocircumferential directions and recessed in the second direction from asurface of the pressure-side cam portion at a side of the firstdirection, the second pressure-side recess being located between thepressure-side assist cam surface and the pressure-side slipper camsurface with respect to the circumferential directions and recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction; at least one of the center-side camportions includes a first center-side recess that is recessed in thefirst direction from a surface of the center-side cam portion at a sideof the second direction; and when seen in an axial direction of theoutput shaft, at least a portion of the first center-side recessoverlaps with the pressure-side cam hole.
 9. A clutch device to allow orinterrupt transfer of a rotation driving force of an input shaft to anoutput shaft, the clutch device comprising: a clutch center housed in aclutch housing holding a plurality of input-side rotating plates to berotationally driven together with the output shaft, the input-siderotating plates being operable to be rotationally driven by rotationaldriving of the input shaft; and a pressure plate movable toward or awayfrom the clutch center and rotatable relative to the clutch center topress the input-side rotating plates and output-side rotating plates,the input-side rotating plates and the output-side rotating plates beingalternately arranged; wherein the pressure plate includes: a body; and aplurality of pressure-side cam portions, assuming a direction in whichthe pressure plate approaches the clutch center is a first direction,and a direction in which the pressure plate moves away from the clutchcenter is a second direction, each of the pressure-side cam portionsprojecting from a surface of the body at a side of the first directionin the first direction, being located radially outward of the outputshaft, and including a pressure-side assist cam surface and apressure-side slipper cam surface, the pressure-side assist cam surfacebeing operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center,the pressure-side slipper cam surface being operable to cause thepressure plate to move away from the clutch center in order to reducethe pressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center;the clutch center includes: an output shaft holding portion to which theoutput shaft is coupled; a plurality of center-side cam portions locatedradially outward of the output shaft holding portion and each includinga center-side assist cam surface operable to generate a force in adirection of causing the pressure plate to approach the clutch center inorder to increase a pressing force between the input-side rotatingplates and the output-side rotating plates upon rotation relative to thepressure plate; and a center-side cam hole penetrating a portion betweenadjacent ones of the center-side cam portions; at least one of thepressure-side cam portions includes at least one of a firstpressure-side recess or a second pressure-side recess, the firstpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect tocircumferential directions and recessed in the second direction from asurface of the pressure-side cam portion at a side of the firstdirection, the second pressure-side recess being located between thepressure-side assist cam surface and the pressure-side slipper camsurface with respect to the circumferential directions and recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction; and when seen in an axial direction of theoutput shaft, at least a portion of the first pressure-side recessoverlaps with the center-side cam hole.
 10. A clutch device to allow orinterrupt transfer of a rotation driving force of an input shaft to anoutput shaft, the clutch device comprising: a clutch center housed in aclutch housing holding a plurality of input-side rotating plates to berotationally driven together with the output shaft, the input-siderotating plates being operable to be rotationally driven by rotationaldriving of the input shaft; and a pressure plate movable toward or awayfrom the clutch center and rotatable relative to the clutch center topress the input-side rotating plates and output-side rotating plates,the input-side rotating plates and the output-side rotating plates beingalternately arranged; wherein the pressure plate includes: a body; and aplurality of pressure-side cam portions, assuming a direction in whichthe pressure plate approaches the clutch center is a first direction,and a direction in which the pressure plate moves away from the clutchcenter is a second direction, each of the pressure-side cam portionsprojecting from a surface of the body at a side of the first directionin the first direction, being located radially outward of the outputshaft, and including a pressure-side assist cam surface and apressure-side slipper cam surface, the pressure-side assist cam surfacebeing operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center,the pressure-side slipper cam surface being operable to cause thepressure plate to move away from the clutch center in order to reducethe pressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the clutch center;and the pressure-side cam portion includes a first pressure-side recessand a second pressure-side recess, the first pressure-side recess beinglocated between the pressure-side assist cam surface and thepressure-side slipper cam surface with respect to circumferentialdirections and recessed in the second direction from a surface of thepressure-side cam portion at a side of the first direction, the secondpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect to thecircumferential directions and recessed in the first direction from asurface of the pressure-side cam portion at a side of the seconddirection.
 11. The clutch device according to claim 10, wherein thepressure plate includes a spring housing portion recessed in thepressure-side cam portion from the second direction in the firstdirection and operable to bias the pressure plate in the firstdirection; and the spring housing portion is located between the firstpressure-side recess and the second pressure-side recess.
 12. The clutchdevice according to claim 10, wherein an end of the first pressure-siderecess in the second direction is located ahead, in the seconddirection, of an end of the second pressure-side recess in the firstdirection.
 13. The clutch device according to claim 10, wherein theclutch center includes: an output shaft holding portion to which theoutput shaft is coupled; and a center-side fitting portion locatedradially outward of the output shaft holding portion; the pressure plateincludes: a pressure-side fitting portion located radially outward ofthe pressure-side cam portions and operable to slidably fit in thecenter-side fitting portion; and an end of the second pressure-siderecess in the first direction is located ahead, in the first direction,of an end of the pressure-side fitting portion in the first direction.14. The clutch device according to claim 10, wherein when seen in anaxial direction of the output shaft, the first pressure-side recess andthe second pressure-side recess do not overlap with each other.
 15. Theclutch device according to claim 10, wherein the clutch center includes:an output shaft holding portion to which the output shaft is coupled;and a plurality of center-side cam portions located radially outward ofthe output shaft holding portion and each including a center-side assistcam surface operable to generate a force in a direction of causing thepressure plate to approach the clutch center in order to increase apressing force between the input-side rotating plates and theoutput-side rotating plates upon rotation relative to the pressureplate; at least one of the center-side cam portions includes a firstcenter-side recess and a second center-side recess, the firstcenter-side recess being recessed in the first direction from a surfaceof the center-side cam portion at a side of the second direction, thesecond center-side recess being recessed in the second direction from asurface of the center-side cam portion at a side of the first direction;and when seen in an axial direction of the output shaft, the firstpressure-side recess of the pressure plate and the second center-siderecess of the clutch center do not overlap with each other.
 16. A clutchdevice to allow or interrupt transfer of a rotation driving force of aninput shaft to an output shaft, the clutch device comprising: a clutchcenter housed in a clutch housing holding a plurality of input-siderotating plates to be rotationally driven together with the outputshaft, the input-side rotating plates being operable to be rotationallydriven by rotational driving of the input shaft; and a pressure platemovable toward or away from the clutch center and rotatable relative tothe clutch center to press the input-side rotating plates andoutput-side rotating plates, the input-side rotating plates and theoutput-side rotating plates being alternately arranged; wherein thepressure plate includes: a body; and a plurality of pressure-side camportions, assuming a direction in which the pressure plate approachesthe clutch center is a first direction, and a direction in which thepressure plate moves away from the clutch center is a second direction,each of the pressure-side cam portions projecting from a surface of thebody at a side of the first direction in the first direction, beinglocated radially outward of the output shaft, and including apressure-side assist cam surface and a pressure-side slipper camsurface, the pressure-side assist cam surface being operable to generatea force in a direction of causing the pressure plate to approach theclutch center in order to increase a pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the clutch center, the pressure-side slipper camsurface being operable to cause the pressure plate to move away from theclutch center in order to reduce the pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the clutch center; at least one of thepressure-side cam portions includes at least one of a firstpressure-side recess or a second pressure-side recess, the firstpressure-side recess being located between the pressure-side assist camsurface and the pressure-side slipper cam surface with respect tocircumferential directions and recessed in the second direction from asurface of the pressure-side cam portion at a side of the firstdirection, the second pressure-side recess being located between thepressure-side assist cam surface and the pressure-side slipper camsurface with respect to the circumferential directions and recessed inthe first direction from a surface of the pressure-side cam portion at aside of the second direction; and assuming a direction from onepressure-side cam portion to another pressure-side cam portion in thepressure-side cam portions is a first circumferential direction and adirection from the another pressure-side cam portion to the onepressure-side cam portion is a second circumferential direction withrespect to the circumferential directions, the pressure plate isoperable to rotate in the first circumferential direction that is adirection from the pressure-side slipper cam surface to thepressure-side assist cam surface of one of the pressure-side camportions, and the first pressure-side recess includes a firstpressure-side slope that tilts to approach the first direction in thefirst circumferential direction.
 17. The clutch device according toclaim 16, wherein the first pressure-side slope is parallel orsubstantially parallel to the pressure-side assist cam surface.
 18. Aclutch device to allow or interrupt transfer of a rotation driving forceof an input shaft to an output shaft, the clutch device comprising: aclutch center housed in a clutch housing holding a plurality ofinput-side rotating plates to be rotationally driven together with theoutput shaft, the input-side rotating plates being operable to berotationally driven by rotational driving of the input shaft; and apressure plate movable toward or away from the clutch center androtatable relative to the clutch center to press the input-side rotatingplates and output-side rotating plates, the input-side rotating platesand the output-side rotating plates being alternately arranged; whereinthe pressure plate includes: a body; and a plurality of pressure-sidecam portions, assuming a direction in which the pressure plateapproaches the clutch center is a first direction, and a direction inwhich the pressure plate moves away from the clutch center is a seconddirection, each of the pressure-side cam portions projecting from asurface of the body at a side of the first direction in the firstdirection, being located radially outward of the output shaft, andincluding a pressure-side assist cam surface and a pressure-side slippercam surface, the pressure-side assist cam surface being operable togenerate a force in a direction of causing the pressure plate toapproach the clutch center in order to increase a pressing force betweenthe input-side rotating plates and the output-side rotating plates uponrotation relative to the clutch center, the pressure-side slipper camsurface being operable to cause the pressure plate to move away from theclutch center in order to reduce the pressing force between theinput-side rotating plates and the output-side rotating plates uponrotation relative to the clutch center; and at least one of thepressure-side cam portions includes a first pressure-side recess locatedbetween the pressure-side assist cam surface and the pressure-sideslipper cam surface with respect to circumferential directions andrecessed in the second direction from a surface of the pressure-side camportion at a side of the first direction.
 19. The clutch deviceaccording to claim 18, wherein the first pressure-side recess includes aperipheral portion parallel or substantially parallel to an edge of thepressure-side assist cam surface located at a distal end of thepressure-side assist cam surface in the circumferential directions, whenseen in an axial direction of the output shaft.